The mucosal sites include the oral cavity, trachea and bronchi, the digestive system and the female reproductive system. The immune responses that develop in these sites are important to fend off potential pathogens. The chemokines are small secreted proteins that regulate the migration of cells of the immune system. We have identified three chemokines (CXCL14, CXCL17 and CCL28) as the most highly expressed in mucosal tissues. We hypothesize that they must have important functions in these mucosal sites. In Specific Aim 1, we will use study the mucosal immune system of mice genetically deficient for each of these chemokines in order to characterize their functions. We already have access to a CXCL14 (-/-) mouse, we can obtain an existing CCL28 (-/-) mouse (available from Deltagen) and we will produce a CXCL17 (-/-) from existing embryonal stem cells where the CXCL17 gene has been inactivated by homologous recombination (available through TIGM). We will also infect these mice with two bacterial pathogens (Chlamydia and Salmonella) to investigate whether these chemokines play a role in immunity against these pathogens. We have already observed that in the CXCL14 (-/-) mouse, the levels of IgA in the gut are severely reduced. Therefore, we hypothesize that CXCL14 is the main chemokine mediating the homing of IgA producing cells to the gut. In Specific Aim 2, we will study the mechanism through which CXCL14 controls IgA production in the gut. We will study whether the IgA-producing cells normally present in the gut exist in these mice. We will also study the M cells as well as the expression of other proteins that have been implicated in gut IgA responses (such as RANKL) as well as for the presence of other immune system cells known to exist in the mouse gut (Th17, Tregs). We will also study whether exogenously administered CXCL14 can reverse the lack of gut IgA in CXCL14 (-/-) mice. Two of these chemokines (CXCL14 and CXCL17) have no known receptors. Therefore, In Specific Aim 3, we will search for their receptors among various orphan G-Protein coupled receptors expressed in two cell types (immature dendritic cells and monocytes) that respond to these chemokines. We will screen by transfecting the GPCRs in appropriate host cells and detecting calcium fluxes specifically induced by the chemokines. Importantly, through these experiments we will identify a new chemokine receptor. Other chemokine receptors have been implicated in human diseases, and represent potential targets for pharmaceutical development. These results will lead to new insights into the role that these as yet unrecognized mucosal chemokines play in the development of mucosal immune responses.